ROBERTSONIAN TRANSLOCATIONS m BRITISH MICE: AN EXPERIMENTAL STUDY. Paul N. Scriven University College London A thesis submitted for the degree of Doctor of Philosophy at the University of London. Department of Biology 1993 ProQuest Number: 10105208 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest. ProQuest 10105208 Published by ProQuest LLC(2016). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. Microform Edition © ProQuest LLC. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 Pangur Ban Written by a student of the monastery of Carinthia on a copy of St Paul's Epistles, in the eighth century (translated from the Gaelic by Robin Flower) I and Pangur Ban, my cat, 'Tis a like task we are at; Hunting mice is his delight, Hunting words I sit all night. Better far than praise of men 'Tis to sit with book and pen; Pangur bears me no ill-will, He too plies his simple skill. 'Tis a merry thing to see At our tasks how glad are we, When at home we sit and find Entertainment to our mind. Oftentimes a mouse will stray In the hero Pangur's way; Oftentimes my keen thought set Takes a meaning in its net. 'Gainst the wall he sets his eye Full and fierce and sharp and sly; 'Gainst the wall of knowledge I All my little wisdom try. When a mouse darts from its den, O how glad is Pangur then! 0 what gladness do I prove When I solve the doubts I love! So in peace our tasks we ply, Pangur Bân, my cat, and I; In our arts we find our bliss, 1 have mine and he has his. Practice every day has made Pangur perfect in his trade; I get wisdom day and night Turning darkness into light. ANON ABSTRACT The processes by which new species are formed have long been open to question. Chromosomal rearrangement has been thought to be important in spéciation. Central to the idea that chromosome rearrangements have a role in spéciation, is that heterozygotes between chromosome races have reduced fertility. A major problem with chromosome spéciation models is that if a rearrangement is effective as an isolating mechanism, it must also have a low probability of being established in a population. This study describes the artificial creation of a house mouse Robertsonian polymorphism on a small island, and the possibility that centric fusions are isolating is investigated. House mice from the Orkney island of Eday (three centric fusions, 2n=34) were released by R.J. Berry and his associates on to the Isle of May, Firth of Forth (standard house mouse karyotype, 2n=40). Within 18 months of introduction each centric fusion had increased in frequency from an estimated starting value of 8% to a value close to 50%, and apparently stabilised three years later with values around 65% for all three fusions, each segregating in accordance with Hardy-Weinberg expectations. The transformed population was behaving as a panmictic unit. Male Eday-May FI hybrids were found to have a relatively low frequency of non-disjunction (13%). Objective data are provided by morphometric analysis of the mandible. Significant changes due to inherited factors were found after a very few generations. Very good agreement was found between single gene loci (represented by allozyme data) and morphology of the mandible. Principal component analysis clearly resolved size and shape differences between the samples and showed post-introduction mice were significantly larger than Eday and pre-introduction May mice, and intermediate in shape. The size difference is a multivariate indication of heterosis (6-8%). 54% of the total post-introduction mandible variation was due to genetic differences. A hybrid index using six blood allozymes (devised to investigate introgression at the level of individual mice), Nei's genetic distance calculated with 19 allozyme loci, and mandible shape, placed post-introduction May mice mid-way between Eday and pre-introduction May. Post-introduction mice were more variable electrophoretically and morphologically than pre­ introduction May mice. The establishment that centric fusions are not strongly underdominant (from the stabilization of a Robertsonian polymorphism, non-significant deviations from Hardy- Weinberg equilibrium, and relatively low rates of non­ disjunction) , means that factors such as deme size, vagility, meiotic drive, inbreeding, and genetic drift, can be revised, and the reality of chromosomal spéciation discounted. CONTENTS PAGE TITLE 1 ABSTRACT 3 LIST OF CONTENTS 5 LIST OF TABLES 6 LIST OF FIGURES 9 ACKNOWLEDGEMENTS 13 PREFACE 14 CHAPTER 1 INTRODUCTION 15 CHAPTER 2 HOUSE MOUSE CHROMOSOMES 29 CHAPTER 3 ELECTROPHORESIS OF BRITISH AND 50 EUROPEAN HOUSE MOUSE POPULATIONS CHAPTER 4 THE ISLE OF MAY 62 CHAPTER 5 INTRODUCTION OF ROBERTSONIAN MICE 65 ON TO THE ISLE OF MAY CHAPTER 6 THE EFFECT OF HYBRIDIZATION ON 79 MANDIBLE MORPHOLOGY CHAPTER 7 DISCUSSION 103 REFERENCES 115 LIST OF TABLES PAGE CHAPTER 2 2.1.1 House mouse Robertsonian translocations 34 found at locations in Europe and North Africa. 2.2.1 Analysis of house mice caught in 38 Caithness. 2.3.1 Robertsonian fusions on Faray. 41 2.4.1 Chromosomes associated with fusions in 44 house mice in Europe and North Africa. 2.4.2 Frequencies of fusions associated with 45 each chromosome in the house mouse. CHAPTER 3 3.1 Electrophoretic data for some European 51 house mouse populations. 3.2.1 Distinguishing electrophoretic alleles 57 in European mice. CHAPTER 5 PAGE 5.2.1 Frequencies of chromosomes and allozyme 71 alleles introduced on to the Isle of May. 5.2.1.1 Estimates of non-disjunction at anaphase 72 I in FI Hybrid, Eday, and May male mice. CHAPTER 6 6.2.1 Age and mandible measurements of pre- 84 introduction May, introduced Eday, and post-introduction hybrid mouse samples. 6.2.2 Comparison of Mahalanobis (D^) and Nei's 85 genetic distances using ten mandible measurements and 19 electrophoretic loci respectively. 6.2.3 Principal component analysis of pooled 86 sample mandible measurements showing component loadings and proportion of the total variation. 6.2.4 Pre-introduction and post-introduction 94 (Sept. 1983) sample variances for means standardized to one. CHAPTER 6 PAGE 6.2.5 Estimates of electrophoretic and 99 morphological variability. CHAPTER 7 7.2.1 Non-disjunction rates of tobacco mouse 108 centric fusions introduced into laboratory strains. LIST OF FIGURES PAGE CHAPTER 2 2.1.1 Principle of Robertsonian translocation 31 2.1.2 Distribution of house mouse Robertsonian 33 populations in Europe and North Africa. 2.2.1 G-banded karyotype of the Caithness house 39 mouse caught at location eight, 2n=32, N.F .=40. 2.2.2 Distribution of house mouse Robertsonian 40 populations in Scotland. 2.6.1 Evolutionary relationships among Rhaethian 49 (North Italian) Robertsonian populations. CHAPTER 3 3.1.1 Cluster analysis of British house mouse 52 populations using the median distance method. 3.1.2 Locations of British house mouse 53 populations used in the electrophoresis study. CHAPTER 3 PAGE 3.1.3 Distributions and frequencies of 54 distinguishing alleles in British house mice. 3.2.1 Cluster analysis of European housemouse 58 populations using the median distance method. 3.2.2 Locations of European house mouse 59 populations used in the electrophoresis study. 3.2.3 Distributions and frequencies of 60 distinguishing alleles in European house mice. CHAPTER 5 5.1.1 G-banded karyotype of an Isle of May 67 house mouse heterozygous for three Robertsonian translocations 2n=37, N.F.=40. 5.1.2 Orcein stained meiotic chromosomes 68 prepared from testis. 10 CHAPTER 5 PAGE 5.2.1 Overall changes in the frequencies of 73 the introduced Robertsonian translocations. 5.2.2 Distributions of introduced centric 74 fusions in Sept. 1983 and Sept. 1986. Each centric fusion had increased significantly in frequency, apparently stabilizing around 65% by Sept. 1986. The transformed population is behaving as a panmictic unit. 5.3.1 Overall changes in the frequencies of 78 centric fusions and allozymes introduced at the same frequency. CHAPTER 6 6.1.1 The 10 measurements made on right 82 mandibles, also showing PGA 2nd component (shape) loadings. 6.2.1 A plot of the first versus second 87 canonical variable showing clear separation of the samples. 11 CHAPTER 6 PAGE 6.2.2 A plot of the first (size) versus 90 second (shape) principal components showing separation of the samples both by mandible size and shape. 6.2.3a Diagrammatic representation of mean 92 mandible size. 6.2.3b Diagrammatic representation of 92 size-corrected mean mandibles - shape (each measurement RMI-RMIO divided by RMIO the greatest length). 6.2.4 Principal component analysis of six 98 allozyme loci (Ada, Car-2. Es-3. Es-10. Gda and Hbb) routinely screened from blood twice per year, showing an increase in frequency of the six introduced alleles, and the attainment of equilibrium at approximately half the frequency found in introduced Eday mice. 12 ACKNOWLEDGEMENTS Thank you to Professor R.J. Berry who made this work possible, for his encouragement and helpful critical comments in the preparation of the manuscript. I thank P. Challinor, R. Nash and P.King for their skilled technical work on the September 83 sample, and Dr. S. Davis for the loan of his "Festingometer".